1. Field of the Invention
The present invention relates to a charged particle beam lithography system and a method for evaluating the same.
2. Description of the Related Art
As semiconductor integrated circuits are highly integrated, LSI patterns are becoming much smaller and complicated. The light exposure is thus desired to use a much smaller exposure mask and reticle used for the LSI patterns. Another proposed method for dealing with such smaller LSI patterns directly draws the LSI pattern by the charged particle beam including an electron beam and an ion beam.
This charged particle beam lithography technology is generally not a batch exposure such as the light exposure using the LSI mask and the like, but a process that scans a substrate with a charged particle beam to draw a pattern thereon. The charged particle beam lithography technology thus takes a time to draw a pattern, providing less throughput.
Some methods are proposed for improving the throughput of the charged particle beam lithography system. Specifically, one method is a stage control method referred to as a step & repeat scheme. This scheme stops the stage during drawing and moves the stage to the next area when a pattern is drawn to a drawable area. The scheme may advantageously use a large charged particle beam deflection area, i.e., a drawable area. The scheme requires, however, time for actually drawing a pattern and additional time for moving to the next drawing area (a non-exposure time). Such a non-exposure time added to the total drawing time reduces the throughput.
Another proposed scheme continuously moves a stage to increase the throughput. This scheme divides the pattern to be drawn into strip-like areas referred to as “frames”. Each frame is drawn while the stage is continuously moved. When the beam reaches the edge of the frame, the stage stepwise moves in a direction perpendicular to the direction of the continuous motion, and a pattern is drawn again while the stage is continuously moved in the opposite direction. This scheme requires a smaller charged-particle-beam deflection area than the step & repeat scheme because a pattern is drawn during the stage motion. This scheme may, however, increase the throughput because the stage stops only at the frame edge.
The charged particle beam may be deflected in a scheme combined with a vector scan scheme (two-dimensional scanning scheme), for further increasing the throughput. The vector scan scheme further divides the frame into areas referred to as “subfields”. Only the necessary portion within the subfield is drawn by the deflected charged particle beam. Unlike the one-dimensional scanning scheme, the vector scan scheme does not scan a non-drawn portion with the turned-off charged particle beam, thus increasing the drawing speed. The vector scan scheme uses a main deflector and an auxiliary deflector. The main deflector positions the charged particle beam to the subfield. The auxiliary deflector draws the subfield by the charged particle beam.
JP 10-284392A describes a drawing method that increases drawing accuracy in the charged particle beam lithography system.